Safety Food in Celiac Disease Patients: A Systematic Review

doi:10.4236/fns.2013.47A008

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Food and Nutrition Sciences, 2013, 4, 55-74

http://dx.doi.org/10.4236/fns.2013.47A008 Published Online July 2013 (http://www.scirp.org/journal/fns)

Safety Food in Celiac Disease Patients: A Systematic

Review

Mariarita Dessì1*, Annalisa Noce2, Sara Vergovich1,3, Gianluca Noce1, Nicola Di Daniele2

1Laboratory Medicine Department, University of Rome Tor Vergata, Rome, Italy; 2Nephrology and Hypertension Unit, Department

of Medicine System, University of Rome Tor Vergata, Rome, Italy; 3Department of Neuroscience, Division of Human Nutrition,

University of Rome Tor Vergata, Rome, Italy.

Email: *mariarita.dessi@uniroma2.it

Received March 28th, 2013; revised April 28th, 2013; accepted May 6th, 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

The prevalence of Celiac Disease (CD), an autoimmune enteropathy, characterized by chronic inflammation of the in-

testinal mucosa, atrophy of intestinal villi and several clinical manifestations has increased in recent years. Epidemiol-

ogical studies have shown that CD is very common and affects about one in 250 people. The mechanism of the intesti-

nal immune-mediated response is not completely clear, but involves an HLA-DQ2 or HLA-DQ8 restricted T-cell im-

mune reaction in the lamina propria as well as an immune reaction in the intestinal epithelium. Subjects affected by CD

cannot tolerate gluten protein, a mixture of storage proteins contained in several cereals (wheat, rye, barley and deriva-

tives). Gluten free-diet remains the cornerstone treatment for celiac patients. Therefore the absence of gluten in natural

and processed foods represents a key aspect of food safety of the gluten-free diet. In this review, we evaluate the main

studies about the safety food in CD patients.

Keywords: Celiac Disease; Safety Food; Gluten Protein; Gluten Free-Diet

1. Introduction

Celiac disease (CD) is an inheritable chronic systemic

autoimmune disorder of the small intestine caused by a

permanent intolerance to gluten proteins in genetically

susceptible individuals [1-2].

Gluten is an alcohol soluble protein fraction present in

cereals such as wheat, rye and barley. The main protein

in wheat gluten is named gliadin; the related protein in

rye and barley gluten are termed horde and secalin, re-

spectively [3]. Gluten contains approximately 15% pro-

line and 35% glutamines residues which limit proteolysis

by gastrointestinal enzymes, thus generating toxic pep-

tides. When the prolamins from these grains are ingested

by an individual with celiac disease, these proteins dam-

age the mucosa of the small intestine, leading to malab-

sorption of nutrients [4].

One of the typical properties of gluten proteins is the

excess presence of the amino acids proline and glutamine.

Proline is responsible for the compact tertiary structure

of gluten. Glutamine residues, carrying an extra amino

group, are deamidated by transglutaminase type 2, which

is activated as part of the first inflammatory response [5].

The ensuing enhanced immune response results in an in-

flammatory reaction in the small-bowel wall. The stages

of this process have been carefully established by Marsh

[6]. Marsh classification: the influx of T lymphocytes

into the epithelium (Stage 1) is followed by the destruc-

tion of mucosa cells, resulting in increased enterocyte

turn-over. At first, increased production ensues as wit-

nessed by crypt hyperplasia (Stage 2), but when the rate

of cell destruction surpasses the rate of cell renewal, also

the villi become shorter leading to increasing severity of

villous atrophy (partial, Stage 3a; subtotal, Stage 3b; total,

Stage 3c) [6].

The first accurate histological description of CD evi-

denced broad flat villi and a dense chronic lympho-

epithelial inflammatory cell infiltrate in the small intes-

tinal mucosa of patients [7]. The persistence of mucosal

injury can lead to serious complications, and gastrointes-

tinal malignancies (particularly lymphoma) have been

reported in 10% - 15% of adult patients with known CD

who do not strictly comply with a gluten-free diet (GFD).

However, the increased risk form malignancy in the gas-

trointestinal tract in patients with CD has been ques-

*Corresponding author.

Safety Food in Celiac Disease Patients: A Systematic Review

tioned recently; therefore, the precise magnitude of this

complication remains uncertain.

The clinical symptoms of CD differ greatly and de-

pend on age of the patient, duration and the extent of ex-

tra-intestinal manifestations [8-10]. Patients with CD

have a wide variety of symptoms: weight loss, chronic

diarrhea, fatigue, delayed onset puberty, abdominal pain,

irritable bowel syndrome, fibromyalgia, dermatitis her-

petiformis, and other extra-intestinal symptoms. In the

oral cavity, enamel defects and recurrent aphthous sto-

matitis are the most common symptoms. Other signs of

malabsorption may occur in the presence or absence of

gastrointestinal symptoms, including iron deficiency ane-

mia, folate deficiency, and osteopenic bone disease and

lymphoma [9].

Genes encoding HLA-DQ2 and HLA-DQ8 molecules

are the single most important predisposing genetic factor.

However, although this polymorphisms are necessary but

they are not sufficient for disease development. HLA-

DQ2 and HLA-DQ8 predispose to disease development

by preferential presentation to mucosal CD4+ T cells of

Pro-rich gluten peptides that have undergone deamida-

tion by the enzyme tissue tranglutaminase [11].

A small intestinal biopsy is necessary to confirm the

diagnosis of CD [12]. Although, the advent of new diag-

nostic serological tests (specific auto-antibodies, IgA

anti-tissue transglutaminase-2, anti-endomysium and anti-

deaminated forms of gliadin peptide antibodies), are widely

used as diagnostic aids in celiac patients and has esti-

mated a prevalence of the disease between 1 in 100 and

200 individuals.

CD was thought to be a rare disease, with a prevalence

of about 0.02%, however using serology and biopsy, re-

cent studies carried out in Europe, India, South America,

Australasia and USA indicate that the prevalence may be

between 0.33 and 1.06% in children and between 0.18%

- 1.2% in adults [13-16]. The highest prevalence (5.66%)

in childhood has been observed in Sahrawi [17]. In other

African countries, CD is rarely diagnosed, this reflects in

a much lower prevalence.

Currently, the only effective treatment for CD is to

maintain a strict gluten-free diet throughout life. How-

ever, is almost impossible to maintain a diet with zero

gluten content because gluten contamination is very com-

mon in food [18].

Oral supplementation with microbial peptidases was

proposed as an alternative to the GFD. These enzymes

are easily inactivated in the stomach by pepsin and acidic

pH, thus failing to degrade gluten before exposure to

small intestine. Hence a combination of glutamine-spe-

cific endoprotease and prolyl-endopeptidase, which rap-

idly detoxifies oligopeptides after primary proteolysis,

was proposed. A new endoprotease from Aspergillus ni-

ger accelerated the degradation of gluten into the stom-

ach to such an extent that only traces reached the duode-

nal compartment. Unfortunately, to date, the safety of the

oral administration of proteases with gluten is yet to be

demonstrated in patients with CD.

Compliance with this dietary prescription results in the

rapid healing of the intestinal mucosa and relief of the

symptoms of malabsorption. Lifelong adherence is gen-

erally promoted to prevent the increases morbidity and

mortality [19], the recurrence of the mucosal lesion and

the appearance of complications related to the disease

such as malignancy, intestinal lymphoma, decreased fer-

tility and skeletal disorders in both men and woman,

growth failure and delayed puberty in children [20]. In

particular, the persistence of mucosal injury can lead gas-

trointestinal malignancies, mainly lymphoma, have been

reported in 10% - 15% of adult patients with known CD

who do not strictly comply with a GFD [21]. However,

the increased risk for malignancy in the gastrointestinal

tract in patients with CD has been questioned recently

and it has been reported that the mortality rate in CD

patients is almost double the rate calculated for the gen-

eral population, mainly because of the occurrence of neo-

plasms. Data from Logan and coworkers [22] have shown

that when appropriate treatment for CD was instituted in

childhood and strictly followed, the mortality rate of

these subjects was no different from that expected in the

general population, and no deaths from intestinal lym-

phoma were recorded. Also CD seems to meet the crite-

ria of a true autoimmune disease for which the genetic

predisposition (HLA), exogenous trigger (gluten), and

autoantigen (Tissue Transglutaminase: tTG) are known.

It seems that tTG is only one of the autoantigens in-

volved in gluten dependent autoimmune reactions. Other

autoantigens that are normally “cryptic” can be unmask-

ed and cause a self-aggressive immunologic response

following the gliadin-initiated inflammatory process. In

fact, persistent stimulation by some pro-inflammatory

cytokines such as interferon-γ (IF-γ) and tumor necrosis

factor-α (TNF-α) can cause further processing of autoan-

tigens and their presentation to T lymphocytes by ma-

crophage-type immunocompetent cells. The phenomenon

of antigen spreading has been described in well-defined

natural models such as insulin-dependent diabetes melli-

tus, whose clinical manifestations appear after the patient

has produced an autoimmune response to various autoan-

tigens, and might also be present in CD. This could ex-

plain the high incidence of autoimmune diseases and the

presence of a large number of organ-specific auto-anti-

bodies in a certain number of celiac subjects on a gluten

containing diet. Based on this evidence, it is tempting to

hypothesize that the range of gluten-dependent autoim-

mune disorders present in genetically predisposed indi-

viduals goes well beyond the classic enteropathy of CD.

Furthermore, recent data suggest that the prevalence of

Safety Food in Celiac Disease Patients: A Systematic Review 57

autoimmune diseases among patients with CD is propor-

tional to the time of exposure to gluten [23]. Patients

with celiac disease also have an increased risk of devel-

oping other autoimmune disorders, such as type I diabe-

tes mellitus [24]. However, it remains unproven whether

trace amounts of gluten are detrimental, provided that the

diet is, on the whole, strict [25].

Refractory Celiac Disease

Celiac disease may be regarded as refractory (RCD)

when symptoms persist or recur after a former good re-

sponse despite strict adherence to a GFD [26-28]. RCD is

define as a persisting villous atrophy with crypt hyper-

plasia and increased intraepithelial T lymphocytes (IELs)

in spite of a strict gluten-free diet for more than 12

months or when severe symptoms necessitate interven-

tion independent of the duration of the diet [29,30]. Im-

munologically, two types of RCD are recognised de-

pending on the presence or absence of aberrant IELs in

the small-bowel mucosa. When normal expression of

T-cell surface markers occurs (RCD I), the prognosis is

less dismal than when an aberrant IEL population is pre-

sent (RCD II). Patients with RCD II are known to be at a

greater risk of developing malignancy, particularly en-

teropathy-associated T-cell lymphoma (EATL) [31-33].

There is now strong molecular and immunophenotypic

evidence showing that a monoclonal neoplastic T-cell

population may emerge from IELs in RCD. Clonal ex-

pansion of this T cell population eventually leads to frank

EATL. The genesis and expansion of these aberrant T

cells involve both inappropriate immune responses to

gluten and acquisition of genetic abnormalities. Although

the IELs in RCD II can be neoplastic, they are not cy-

tologically abnormal and do not form tumour masses that

differentiate these patients from EATL patients, in addi-

tion to the absence of radiological and bone marrow evi-

dence of lymphoma [34-37].

RCD II is usually resistant to any known therapy that

has thus far been tested, including azathioprine/predni-

sone, cyclosporine and interleukin-10 (IL-10) [38-43].

In a retrospective study the authors evaluate the course

of RCD and EATL in a large cohort of patients with

complicated celiac disease. In particular, they have ret-

rospectively compared the survival in four groups of pa-

tients: RCD-I, RCD II total, secondary EATL and de

novo EATL and performed a retrospective analysis, pro-

viding long-term follow-up data on four categories of

patients with complicated forms of celiac disease. In the

present study were enrolled 43 patients with RCD I; 50

with RCD II (total), of whom 26 with RCD II developed

EATL after a period of refractoriness to a gluten-free diet

(secondary EATL) and 13 were EATL patients without

preceding history of complicated celiac disease (de novo

EATL). The investigation has showed these results:

 No celiac-disease-related mortality was recognised in

the RCD I group;

 The overall 5-year survival in the RCD I group it was

96%; in the RCD II (total) group was 58%; and in the

RCD II group after developing EATL it was only 8%;

 The 2-year survival in the de novo EATL group was

20% versus 15% in secondary EATL group (p =

0.63);

 Twenty-eight (56%) of the 50 patients with RCD II

died, 23 (46%) due to EATL, 4 due to a progressive

refractory state with emaciation and 1 from neuro-

celiac disease.

Remarkably, no patient with RCD I developed RCD II

or EATL within the mean follow-up period of 5 years

(range 2 - 15 years). A total of 52% of the RCD II pa-

tients developed EATL within 4 - 6 years after the diag-

nosis of RCD II.

In conclusion, an extensive evaluation and aggressive

targeted therapies might be helpful in dealing with com-

plicated forms of celiac disease. Studies are needed to

define more precisely the cut-off point between accepta-

bly normal and pathologically increased percentages of

aberrant T-cells [44].

2. History of Dietary Prescription for Celiac

Disease

In the late 19th and early 20th centuries, it was common

to prescribe fruit-only diets, fruit and vegetable diets and

banana diets at celiac patients [45].

In the 1930s and 1940s, William K. Dicke observed

that his patient’s symptoms improved when wheat was

removed from their diet [46]. They used fecal fat analysis

and they found that some starches, as wheat flour, rye

flour, oats, were harmful for celiac patients, others, as

wheat starch, corn flour, maize starch, rice flour, peeled

boiled potatoes, were not [46]. Because wheat flour was

shown to be harmful and wheat starch was not, they con-

cluded that the offending agent was not in the starch

component of the grain, but was the gluten, in particular

the gliadin component of gluten, that was responsible for

the harmful effects of wheat flour [45].

The standard dietary prescription for celiac patients

remains essentially the same as it was 40 years ago, and

this diet appears simple to follow (they must avoid all

sources of wheat, rye, barley, and oat prolamins), but is

actually quite complex when all sources of these prola-

mins are considered.

In fact, obscure sources may include flavorings, spices,

fillers, and condiments [47-48].

The term Gluten free diet may give the false impres-

sion that gluten is found in all cereal grains toxic to per-

sons with celiac disease. In actuality, gluten refers spe-

Safety Food in Celiac Disease Patients: A Systematic Review

cifically to the protein complex composed of the prola-

min, gliadin, glutelin and glutenin, and is found only in

wheat [49]. The term Gluten free is used to describe a

food or diet devoid not only of wheat but also of all

grains containing the offending prolamins believed to be

associated with celiac disease [49].

2.1. Identifying the Toxic Factor

It is generally believed that the toxic factor in celiac dis-

ease is found in the gliadin fraction of gluten [4,50].

Gliadin has been broken down into several sub-frac-

tions, and although α-gliadin is often recognized as the

most toxic, it is not yet clear which fractions contain the

offending peptides [50,51]. Although the precise amino-

acid sequence in wheat gliadin responsible for activating

celiac disease are still being determined, attention has fo-

cused recently on two proteins: the tetrapeptides proline-

serine-gliutamine-glutamine and glutamine-glutamine-glu-

tamine-proline [52]. The last one of these tetrapeptides is

found in three of the gliadin subfractions and in certain

subunits of secalins (rye), hordeins (barley), and avenins

(oats) [52].

2.2. Differences in the Chemical Make-Up of

Grains

There are numerous differences in chemical make-up

between the grains that may activate celiac disease, as

wheat, rye, barley, and the grain with questionable toxic-

ity, as oats:

 Rye and barley are more closely related taxonomi-

cally to wheat than are oats [4];

 Rye and barley prolamins share substantial sequence

homology with wheat prolamins, whereas oat prola-

mins do not [50];

 Barley, hordeins and rye secalins seem to be related

antigenically to wheat gliadin, while oat avenin does

not [51];

 Although wheat, rye, barley, and oats contain ap-

proximately the same amount of total protein, they do

not contain the same amount of prolamin [53].

Oat prolamins account for only 10% to 15% of total

protein, whereas those of wheat, rye, and barley account

for 40% to 50%, 30% to 50%, and 35% to 45% of total

protein, respectively.

Even if oat avenin contains the factor responsible for

the toxicity seen in celiac disease, it would take a much

larger intake of oats than of wheat, rye, or barley to bring

about the same toxic effect [53].

2.3. Oat Studies

In 1953 W. K. Dicke [46] saw that oats had a negative

effect on their patience with CD. Since that time, several

studies have been designed in order to assess the toxicity

of oats. In 1995, Finnish investigators published the first

randomized trial comparing diets with and without oats

in adults with celiac disease [54,55]. They demonstrated

that adding a moderate amount of oats (about 50 g/d) to a

gluten free diet allowed symptomatic and histological

remission in adults newly diagnosed with celiac disease

after 12 months and no deterioration after 6 months in

patients with celiac disease in remission.

In other more recently paper, K. Holm [56] and col-

leagues studied the long-term safety of oats in the treat-

ment of children suffering from CD. In this study 32

children with CD were enrolled in a 2-year controlled

trial. The results showed that in celiac children in remis-

sion, oats had not detrimental effect on intestinal histol-

ogy or serology during the 2-year trial. In conclusion the

authors have seen in most of children with CD that the

long-term consumption of oats is well tolerated, and it

does not result in small bowel mucosal deterioration or

immune activation (Table 1).

Moreover, oats are known to be a source of both solu-

ble and insoluble dietary fiber, B-complex vitamins (thia-

min, niacin and riboflavin), iron and proteins [57,58].

However, the safety of oats as part of gluten free diet has

been an object of debate because there is evidence to

indicate some individuals with CD are intolerant to oats

in addition to wheat, barley and rye [59].

The complexity of CD along with a certain homology

in the protein fraction of oats with other gluten-contain-

ing cereal is likely to be the reason why some individuals

react to oats.

Although there is a significant difference between the

proteins found in oats and the immuno-stimulatory pro-

tein sequences found in wheat, rye and barely which may

explain why most people with CD are able to tolerate

these cereal grains [60]. There are a lot of evidences to

suggest that pure oats (uncontaminated with other gluten-

containing cereal grains) are safe to consume in moderate

amounts by most people with CD, as it is an important

source of proteins, carbohydrates and fiber [61].

T. B. Koerner et al. studied the gluten contamination

in the Canadian commercial oat supply [62]. The major-

ity of people with CD and on gluten-free diet can safely

consume pure oats, however previous studies have indi-

cated that the commercial oat supply in other countries,

and in Canada to some extent, is contaminated with other

grains. To obtain a better picture of gluten contamination

within the oat varieties sold at Canadian retailers the au-

thors collected a large sampling from across the country

for a variety of different oat products. Gluten analysis was

performed in duplicate using the RIDASCREEN R-7001

gliadin ELISA (enzyme-linked immunosorbent assays).

Of the 133 samples analyzed only nine (6.8%) were

ound to contain levels of glten below the 20 mg·kg−1 f

Safety Food in Celiac Disease Patients: A Systematic Review

Table 1. Characteristics of included studies on oats effects.

Author Study design N patientsPopula tionOutcome methods Effects of oats

K. Holm et al. [56] Controlled long-term trial 32 ChildrenSmall bowel biopsy, serology parameters No toxic

M. Silano et al. [59] Prospective study 10 ChildrenLymphocyte proliferation, IFN-γ in culture

medium Uncertain toxicity

Sey et al. [63] Prospective study 15 Adults Duodenal biopsy No toxic

E. K. Janatuinen et al. [64] Randomized trial 92 Adults Small-bowel biopsy No toxic

E. K. Janatuinen et al. [65] Long-term trial 92 Adults Duodenal biopsy, antiendomysial,

antireticulin, antigliadin Ab No toxic

Sey et al. [68] Cohort study from Canada 15 Adults Symptoms, small-bowel biopsy, tTG No toxic

I. Comino et al. [69] Case-control study 10 patients

5 controlsAdults Small-bowel biopsy, serological analysis Oat immunogenicity

limit proposed by the Codex Alimentarius Commission

for naturally gluten-free foods. Three of these samples

had undetectable amounts of gluten, while the remaining

samples were between 5 and 20 mg·kg−1. The remaining

samples (n = 124, 93.2%) showed contamination levels

above this limit and ranged from approximately 21 to

3800 mg·kg−1. Previous studies that have measured the

gluten content in oats had a limited number of samples

from the Canadian market, but showed similar contami-

nation levels to this study.

M. Sey et al. [63] demonstrated the safety of pure and

uncontaminated oats fed for 12 weeks to 15 adults with

well controlled celiac disease. However, the possible

contamination with wheat, barley and rye limited their

use.

The Canadian Celiac Association recently released

guidelines governing the production of pure oats. In fact,

oats were excluded in the GFD until recently, when E. K.

Janatuinen et al. [64] demonstrated the safety of pure,

uncontaminated oats in celiac disease. They examine two

types of patients: those newly diagnosed with celiac dis-

ease (n = 40), and those in remission (n = 52). Study par-

ticipants were randomized to one of two diets: a conven-

tional GFD or a conventional GFD plus the addition of

50 - 70 g oats. At the end of the 6 and 12 month study

periods, investigators found no adverse effects on the in-

testinal mucosa of patients in remission. Among patients

who were newly diagnosed a dietary intake of oats for 12

months did not prevent the intestinal mucosa from heal-

ing. The study population was re-examined after 5 years

to determine whether there were any adverse effects after

a long term consumption of oats. The investigators con-

cluded that there were no statistically significant differ-

ences in duodenal villous architecture or mononuclear

cell infiltration between the two groups.

Other studies have not found harmful effects due to the

addiction of pure oats to the GFD [65]. The common oat,

Avena sativa, has a multitude of nutrition benefits: as a

rich source of fiber, helped to promote bowel regularity,

attenuated post-prandial glycemic response in diabetic

patients, improved lipid profiles, and possibly reduced

cardiovascular risk [66]. Despite its nutrition benefits, re-

ports of oat contamination with other grains limited its

consumption.

In a recent study examining the purity of 109 commer-

cially available oat products in the United States, Canada,

and Europe, 71% were contaminated with wheat, rye or

barley [67].

Other study performed on fifteen adult patients with

biopsy-confirmed celiac disease, asymptomatic on a GFD

for at least 1 year and having a normal tTG. There were

no significant changes in symptoms, biochemistry, or

histology after oat challenge. The limitation of this study

are: the use of random food diaries to monitor for com-

pliance to a GFD (a self-reporting method with potential

bias), the length of follow-up (12 weeks, time sufficient

to allow a histological response to our oat challenge), and

the small sample size, only fifteen. Although the result of

the study support the safety of oats manufactured under

the Canadian Celiac Association Guidelines, future stud-

ies with larger sample sizes are needed to prove beyond

95% certainty that these products are indeed safe in pa-

tients with celiac disease [68].

Recently investigators confirmed that oat immuno-

genicity for patients with celiac disease varies between

the avenins of different varieties (cultivars) of oats [69].

The injury attributed to oats in celiac disease is, in most

cases, likely due to wheat, rye or barley contamination

[60].

Since many studies have shown that there weren’t ad-

verse effects associated with the regular consumption of

moderate amounts of oats, some organizations have

changed their recommendations regarding their con-

sumption. For example, the Finnish Celiac Society [70],

as well as United Kingdom Celiac Society [71], consid-

ered oats safe for consumption by adults.

However, the latter organization recommends that cer-

tain restrictions be placed on the use of oats, only adults

well established CD patients on a gluten free diet and

less than 50 g per day. It also suggested that only oat

Safety Food in Celiac Disease Patients: A Systematic Review

products free of contamination from other grains (as

wheat, rye, and barley) be used [72].

Despite this, in North America all major celiac organi-

zations continue to advice against the use of oats [73-75].

While the oats seem to be devoid of toxicity, they contain

harmful amino acid sequences, because the cross reactiv-

ity of oat prolamins with antibodies to wheat gliadin and

the ability of oat prolamins to activate an immune re-

sponse in intestinal biopsy specimens in vitro [75]. In

addition there are concerns that even if oats do not con-

tain harmful aminoacid sequences, they nonetheless may

became contaminated with wheat, rye, or barley before

reaching the consumer; in fact because the same equip-

ment may be used for a variety of grains, it is possible

that oats may became contaminated with harmful prola-

mins while being harvested, transported, stored, milled,

or processed [76].

Only in two recent studies, the authors used commer-

cial oat products to assess the safety of oats [77] while in

the most of investigations used oats that were tested

found to be free of contamination [78]. From a careful

meta-analysis on the safety of oats, concluded that most

CD patients can consume moderate amounts of uncon-

taminated oats without causing damage to the intestinal

mucosa. Unfortunately, we do not know the minimum

amount of harmful prolamin taken, and for what period

of time has been consumed: is necessary to bring about

histologic changes to the intestinal mucosa [79].

The problem of contamination affects not only the oats

but also other gluten free foods [80]. As oats are not en-

dorsed for use in the United States, there isn’t market

demand to identify uncontaminated oat products. As with

other gluten free foods, the risk of consuming contami-

nated oat products could be lower if persons with celiac

disease consumed only products milled and processed in

a dedicated facility as those of Mc- Cann’s brand (Naas,

Ireland), although they will not absolutely guarantee that

their oat products are free of contamination [81].

Finally the ideal would be to consume only those pro-

duct tested and found to be free of contamination. If this

is not possible, patients should be counseled on steps

they can take to help reduce their changes of consuming

contaminated oat products.

3. Gluten-Free Diet

GFD has been accepted as an effective therapy in symp-

tomatic CD patients, but life-long treatment in some cli-

nical forms of CD (e.g., latent or potential) may be diffi-

cult to achieve [82].

The diet may be low in fibre, iron, folate, calcium,

magnesium, zinc, B-complex vitamins (thiamine, ribo-

flavin, niacin, and vitamin B12), as well as vitamin D

[83,84].

L. Kinsey et al. [85] demonstrated that celiac patients

adhering to a GFD may be at risk for inadequate intake

of calcium, non-starch polysaccharides, and vitamin D.

Evaluation of self-reported food-records demonstrated

insufficient daily doses of these substances in the GFDs

of both male (calcium 63%) and female (calcium 31%,

iron 66%, fibre 46%) celiac patients in the United States

[86]. These findings demonstrate that the nutritional qua-

lity of GFDs should be considered.

A. L. Lee et al. [87] compared a “standard GFD” (na-

turally gluten-free grains and products) and an “alterna-

tive GFD” (oats flour, high-fibre gluten-free bread, and

quinoa). The alternative grains provided a significantly

higher nutritional profile. Oats of kilned as well as un-

dried varieties can increase intakes of vitamin B1, mag-

nesium and zinc in remission celiac patients [88].

Oats are unique among cereals for their multifunc-

tional characteristics and nutritional profile [89]. Fur-

thermore they are a good source of dietary fibre (particu-

larly in the form of soluble beta-glucan), minerals, vita-

mins and other nutrients.

The absence of gluten in natural and processed foods

represents a key aspect of food safety of the gluten-free

diet [90].

Previous studies have investigated the nutritional com-

position of processed gluten-free products and it has been

demonstrated that they have high levels of lipids, sugars

and salt.

The relationship between the disease and the ingestion

of wheat gluten proteins has became an essential part of

the definition of “Gluten Free Diet”, GFD means that CD

subjects have to exclude all food cereals including pasta,

breads and crackers are not allowed. Malt is also toxic

for CD subjects because it is a partial hydrolysate of bar-

ley prolamins [91]. Therefore barley malt, malt syrup,

malt extract, malt flavorings cannot be inserted in CD

diet. The use of oats in GFD is still debated in relation to

a possible cross-contamination with gluten-containing

grains, as demonstrated in some commercial products in

the United States. However, some studies have demon-

strated gluten contamination either in naturally gluten

free products (soybean, rice, millet, corn, buckwheat) or

in industrially-purified gluten free flours, recent studies

have revealed that when consumed in moderation, oat

free from cross-contamination with gluten-containing

grains, is well-tolerated by most children and adults with

CD.

In the last years, the range of processed gluten-free

products is increased: breads, biscuits, and pasta pro-

duced by gluten-free ingredients and food additives have

been proposed on the market. Therefore, celiac patients

need to pay attention to food labels, looking for words

such as wheat starch, wheat bran, graham flour, kamut

and hydrolyzed wheat protein.

Safety Food in Celiac Disease Patients: A Systematic Review 61

Unfortunately, gluten contamination in processed GF

products cannot be totally avoided. There is no agree-

ment about the amount of dietary gluten that CD subjects

may introduce without damaging the mucosa of the small

intestine. Some authors consider safe a threshold of less

than 30 mg of gluten per day [18]; between 10 and 100

mg intake daily [92]; higher than 50 mg per day [93].

Previous studies have demonstrated that gluten free

diet products are poor sources of minerals (such as iron),

vitamins (such as folate, thiamine niacin and riboflavin)

and fiber [84], therefore the nutritional content of gluten-

free. A promising area is the use of minor or pseudo-

cereals such as amaranth, buckwheat, quinoa, sorghum

and teff. Minor cereals and pseudo-cereals may be used

to prepare several gluten-free specialty products, and

they are important sources of proteins and carbohydrates,

especially fiber, and can contribute to reduce nutritional

deficiencies of treated CD subjects and decrease prices of

gluten free foods. The technological and nutritional prop-

erties of these alternative cereals as wheat replacements

have been investigated and it has been suggested that

their use could improve intakes of protein, iron, calcium

and fiber of celiac patients [87].

In a systematic review of literature on oat inclusion in

the gluten-free diet, S. Størstud et al. [94] noted that the

inclusion of oats would increase the variety and nutrient

content of the gluten-free diet. Other authors confirmed

that oats had a positive effect on GDF [88].

Recently, A. R. Lee et al. [87] demonstrated that the

addition of gluten-free alternative grains, including oats

and quinoa, positively impacts the nutrient profile (fiber,

thiamine, riboflavin, niacin, folate and iron) of the grain

portion of the gluten-free diet.

3.1. Gluten-Free Diet: Imprudent Dietary Advice

for the General Population?

Between 2004 and 2011 the market for gluten free prod-

ucts grew at a rate of 28% per annum [95] and this num-

ber is intended to increase in the coming years, because

consumers are perceived to be healthier than their gluten

containing counterparts [96]. Gluten free diets are indi-

cated for patients with celiac disease, for person with

gluten sensitivity, and for individuals with chronic auto-

immune disease such as psoriasis, rheumatoid arthritis

and type 1 diabetes [97].

Luckily, with the growth in the gluten free products

marked, a greater number of food choices are available to

individuals for whom gluten avoidance is essential. There

are many gluten free grains available to help consumers

obtain the benefits of whole grains and overcome some

of the nutritional deficiencies (as inadequate intakes of

thiamin, riboflavin, niacin, folate and iron) associated

with gluten free diet [98,99].

3.2. Difficulty Following a GFD in Celiac Disease

Patients

Individuals have difficulty following a gluten free diet

because several of reason, such as:

 Poor attitude toward the diet;

 Diet’s social and psychological burden;

 Conflicting information from difference sources about

how to follow a GFD;

 Travelling and dining out;

 Unknown presence of gluten in nonfood products

such as medications;

 Food labeling that does not specifically describe the

levels of gluten [100,101].

It is difficult to avoid gluten because is found in many

packaged processed foods, in some medicines and die-

tary supplements. Since most gluten found in food is

derived from wheat, in the USA if a products regulated

by the FDA (Food and Drug Administration) contain

“wheat” protein, the term wheat must be properly de-

clared on the product label in the ingredients list. This

labeling requirement was established by the Food Aller-

gen Labeling and Consumer Protection Act (FALCPA)

that defined wheat as a major food allergen. In the USA

individuals need to be familiar with the names of ingre-

dients that contain gluten derived from non-wheat

sources, for example malt and malt extract derived from

barley.

An increasing number of food on the marked bear

gluten free claims. In 2007 FDA, with the collaboration

of FALCPA, published a proposed rule identifying to

define the term Gluten free for voluntary use on the la-

bels of food: a food labeled GF cannot contain 20 or

more parts per million (ppm) of gluten [102].

Regulations in Europe on use of GF on the food label

went into effect in January 2012, when the European

Commission set levels for usage of GF at 20 ppm or less.

Furthermore, the term “very low gluten” is used on the

food label when gluten content is greater than 20 ppm

but no more of 100 ppm. Consuming more package proc-

essed foods might increase the amount of time spent on

food shopping or reading the food label to ensure the

product is safe to consume or does not contain gluten.

4. Safety and Contamination of Food for CD

Patients

4.1. Magneto Immuno-Sensor for Gliadin

Detection in Gluten-Free Foodstuff

The treatment of celiac disease is a GFD, for this reason,

gluten has been included in food labeling, in order to

prevent harmful effects of gluten containing food or food

components in celiac patients [103].

The FDA in the USA, defined in 2008 that foods la-

Safety Food in Celiac Disease Patients: A Systematic Review

beled with the term gluten free may not exceed gluten

content of 20 mg/L [104]. The same regulation has been

taken in 2009 by the European Community [105]. It is

really important to have reliable methods for the detec-

tion of gliadin both for celiac patients than for the indus-

tries generating gluten free foodstuff in order to rapidly

test incoming raw materials and check for gluten con-

tamination throughout the food production process [106,

107].

The most commonly used methods for gliadin meas-

urements are based on immunological procedures: ELISA,

using monoclonal or polyclonal antibodies against a va-

riety of gliadin components [108]. Different ELISAs in

sandwich format are commercially available: this is con-

sidered the official method of the Association of Ana-

lytical Communities and is based on a monoclonal ω-

gliadin antibody that is able to recognize the heat stable

ω fraction from wheat, rye, and barley prolamins [109].

Another method for gluten determination is based on a

monoclonal R5 antibody and is accepted by the Codex

Alimentarius Committee [110].

The developments of immunosensors are promising

alternatives to the immunochemical tests to ensure food

safety from farm to table in Hazard Analysis and Critical

Control Points (HACCP) [111]. This field of research is

focused on the development of an electrochemical mag-

neto-immunosensors for the sensitive detection of gliadin

of small gliadin fragment in natural or pretreated food,

and also in gluten free food samples. The performance of

the electrochemical immunosensor is compared with a

novel magneto ELISA with optical detection for the de-

termination of gliadin in complex food samples such as

skimmed-milk and gluten free beer. The magneto-im-

munosensor combines the advantages taken from immu-

nochemical assays and magnetic beads separation with

the sensitivity and robustness of the electrochemical de-

tection. For this reason, the electrochemical magneto im-

munosensor is suitable for the rapid analysis of gliadin in

foodstuff.

4.2. Characterization of Monoclonal Antibodies

to a Main Immunogenic Gluten Peptide

Among the main dietary proteins, the gluten is unique as

it contains a high content of proline and glutamine, (ap-

proximately 15% of proline and 35% glutamine) [112].

This high proline and glutamine content prevents com-

plete proteolysis by gastric and pancreatic enzymes, such

that long oligopeptides, that are toxic to CD patients,

build up in the small intestine. One peptide in particular,

the 33-mer from a-2 gliadin (residues 57-89), contains 6

T-cell epitopes, is highly proteolytically resistant [113].

At present, the prescription of a gluten-free diet is the

only therapy for CD patients. However, it is not easy to

maintain a diet with zero gluten content because gluten

contamination is commonplace in food [18]. Gluten is a

common ingredient in the human diet; after sugar, it is

perhaps the second most widespread food substance in

Western civilization. Since about 10% of gluten seems to

be made up of potentially toxic gliadin peptides [114], it

is desirable to quantify the amount of these peptides in-

gested by a CD patient, so that the factual toxicity of the

gluten present in foods can be established more precisely.

The 33-mer peptide from α2-gliadin is a principal con-

tributor to gluten immunotoxicity [110]. Thus the pro-

duction of monoclonal antibody (moAbs) against this

toxic gluten peptide could be of great importance in both

research and diagnosis. The ability of G12 and A1 to

detect oats is of potential practical importance.

Oats cause damage to the mucosa in a subset of CD

patients [114,115]. In contrast to previously described

anti-prolamin moAbs (e.g. R5 and anti-glia-a2/9) [110,

116,117], G12 and A1 both detected oats although with

lower sensitivity than the prolamins from wheat, barley

and rye. The A1 competitive ELISA developed would

enable the detection of the presence of gluten in food-

stuffs at values as low as 0.33 ppm of gluten, which is far

below the 20 ppm threshold proposed by the Codex Ali-

mentarius Commission [118]. The recommended maxi-

mum daily ingestion of gluten is below 50 mg gluten per

day. The method reported previously could detect several

orders of magnitude less concentration than the maxi-

mum recommended gluten concentration in the digestive

tract (20 mg/L) for CD patients [93].

4.3. Sensitive Detection of Cereal Fractions That

Are Toxic to Celiac Disease Patients by

Using Monoclonal Antibodies to a Main

Immunogenic Wheat Peptide

Moron e coworkers [119] developed immunologic assays

as a novel food analysis in order to measuring cereal

fractions that are immunotoxic to CD patients. This work

focused the attention on the production of monoclonal

antibodies against the gladin 33-mer peptide and the de-

velopment of ELISA and Western blot analysis with the

use of novel antibodies. A sandwich ELISA method

showed a detection limit for wheat, barley, and rye of <1

ppm prolamine. However, the method required a sample

that was ≥1 order of magnitude greater for the detection

of low-toxic oats, and there was no signal with the safe

cereals maize and rice. A competitive ELISA method

was also developed for detection of the toxic peptide in

hydrolyzed food, which had a detection limit of <0.5

ppm gladin. Both ELISAs designed for use with the toxic

gladin 33-mer peptide suggested a high correlation be-

tween the presence of the peptide and the amount of ce-

real that was toxic to CD patients. The sensivity was sig-

nificantly higher than that of equivalent methods recog-

nizing other gluten epitopes.

Safety Food in Celiac Disease Patients: A Systematic Review 63

4.4. Characterization of Cereal Toxicity for

Celiac Disease Patients Based on Protein

Homology in Grains

In this study the purpose of the authors was to found for

such peptides based on the assumption that gluten-spe-

cific-T-cells might cross-react with homologous peptides

in barley, rye, and/or oats. Apart from the glia-γ2 epitope

[119], none of the other T-cell stimulatory gluten pep-

tides had an identical match in the hordeins, secalins, or

avenins. Several of these peptides stimulated gluten-

specific and this was the demonstration that T-cell cross-

reactivity between gluten peptides and related peptides in

the hordeins and secalins can be related to the toxicity of

barley and rye for patients with CD. T-cell reactivity

against additional peptides, that are exclusively present

in hordeins and/or secalins, could aggravate the T-cell

response on ingestion of these grains by patients. The

lack of proline residues in avenin molecules results in

higher susceptibility of the oats proteins for degradation

by proteases in the gastrointestinal tract. In fact, the only

peptides that are clearly sensitive to breakdown are the

avenin-γ2 peptides that are cleaved by elastase. The rapid

degradation of potential harmful avenin peptides may

help to prevent the initiation of an immune response

against oats in the small intestine. Notably, the treatment

of gluten with an enzyme specific for proline rich se-

quences has recently been suggested to destroy the toxic

properties of gluten [113]. The results of this study indi-

cated that the unique composition of cereal proteins that

contain high amounts of glutamine and proline residues

is the basis of the toxicity of wheat, barley, and rye for

patients with celiac disease. Strategies to detoxify wheat

and other cereal proteins should therefore first select

these less-immunogenic gluten molecules and subse-

quently focus on the elimination of residual T-cell stimu-

latory sequences. The authors showed that the substitu-

tion of a proline residue with a glutamine residue can

destroyed the T-cell stimulatory capacity of a gluten pep-

tide. In conclusion, it was characterized novel T-cell sti-

mulatory sequences in barley and rye on the basis of

T-cell cross-reactivity with gluten proteins. Such cross-

reactive T-cell responses are likely to play a role in the

observed toxicity of these cereals for patients with celiac

disease. Moreover, the subtle changes in gluten genes

would eliminate some of the T-cell stimulatory properties

of gluten molecules.

4.5. The Safe Threshold for Gluten

Contamination in Gluten-Free Products.

Can Trace Amounts Be Accepted in the

Treatment of Celiac Disease?

In recent study, the intent of the authors was to estimate a

reasonable limit for residual gluten in gluten-free prod-

ucts on the markets. The gluten content was determined

in the most widely used naturally gluten-free and wheat

starch-based gluten-free flours and baked products. In

this study the gluten content of 59 naturally gluten-free

and 24 wheat starch-based gluten-free products were

analyzed by ELISA. The daily intake of flours was cal-

culated in 76 adults on gluten-free diet, and the intake

compared with mucosal histology. Trace amounts of glu-

ten were found in both naturally gluten-free and wheat

starch-derived flours, 42 of 59 and two of 24 were free of

gluten contamination (<10 ppm), respectively. Five natu-

rally gluten-free and two wheat starch-based products

contained more than 100 ppm gluten; none exceeded 200

ppm.

The results showed that a number of both naturally

gluten-free (13 of 59) and wheat starch-based gluten-free

(11 of 24) products contained gluten from 20 to 200 ppm.

The median daily flour consumption was 80g (range: 10 -

300). Within these limits, the long-term mucosal recov-

ery was good. The threshold for gluten-contamination

can safely be set at 100 ppm. Provided that the daily

flour intake is even 300 g, a level of 100 ppm results in

30 mg of gluten intake. This has been shown to be safe,

when correlated to histology, in clinical and challenge

studies. In this study has been ascertain that most wheat

starch based gluten-free products contain trace amounts

of gluten after taking wheat starch-based gluten-free

products in an open study design have been reported only

occasional abdominal complaints but no intestinal mu-

cosal deterioration.

They therefore concluded that these products were safe

in clinical practice [120].

This was also verified in a prospective controlled

study where no differences in histology, serology or qua-

lity of life were seen between wheat starch-based and

naturally gluten-free products [25].

K. Kaukinen et al. have occurred if patients with CD

can safely consume wheat-based starch hydrolyzed prod-

ucts, since the safe threshold for gluten in gluten-free

products is under investigation [121].

P. Collin et al. reported that industrially purified wheat

starch-based gluten-free products have been shown to

contain trace amounts of gluten (0 - 150 mg/kg = ppm

gluten) [18]. Although the products have proved safe in

clinical practice, [25,122-124], some authorities recom-

mend only cereals, which are gluten-free by nature

(maize, rice, buckwheat), for the treatment of celiac dis-

ease [125]. Their objective has been to establish whether

wheat-based starch hydrolysates (glucose syrups and

malto-dextrins) have untoward effects on small-bowel

mucosal morphology or inflammation, serology or symp-

toms in CD patients. This was important to ensure that

CD patients can safely continue to consume these type

products in their GFD.

Safety Food in Celiac Disease Patients: A Systematic Review

In a randomized, double-blind, placebo-controlled,

prospective follow-up study involved 90 celiac disease

patients in remission randomized to consume glucose

syrups, maltodextrins or placebo for 24 weeks. The au-

thors controlled small bowel mucosal morphology and

inflammation, symptoms, celiac serology at baseline and

after 24 weeks with laboratory analysis, gastroscopy and

duodenal biopsy and clinical evaluation. Only four of the

90 patients did not consent to complete the last study

visit and follow-up small-bowel biopsy. However, when

they hypothesized that if these four patients would have

developed abnormal small bowel mucosal morphology

with total villous atrophy and massive inflammation, the

main results of the study did not change. The authors

found that daily ingestion of wheat-based starch hydro-

lysates had no deleterious effect on small-bowel mucosal

villous architecture or inflammation, serology, gastroin-

testinal symptoms or malabsorption parameters in celiac

disease patients. Daily ingestion of wheat-based starch

hydrolysates, glucose syrups and maltodextrins, had no

deleterious effect on small-bowel mucosal villous archi-

tecture or inflammation in CD patients when compared

to the placebo group. Neither were there any significant

differences in gastrointestinal symptoms, serology or

malabsorption parameters after 24 weeks. Maltodextrins

didn’t have any deleterious effect on celiac disease pa-

tients when compared to the subjects in the placebo

group. Even in the placebo group there were clear chan-

ges in small-bowel mucosal morphology and inflamma-

tion during the study.

According to the literature, some patients having long-

term treated celiac disease may have abnormal small-

bowel mucosa or positive celiac serology, despite a strict

gluten-free diet [93,125,126]. In this study patients have

evinced an excellent response to a strict gluten-free diet,

even though they had consumed wheat starch-based

flours and hydrolysates for years before the present in-

tervention study, and they remained in good remission

after 6 months additional daily challenge with wheat

starch-based hydrolysates. To conclude wheat-based starch

hydrolysates, glucose syrups and maltodextrins did not

have harmful effect on celiac disease patients and they

safely continue to consume these products.

4.6. Duration of Exposure to Gluten and Risk for

Autoimmune Disorders in Patients with

Celiac Disease

The relationship between celiac disease and many auto-

immune disorders has been explained by the sharing of a

common genetic factor. Ventura et al. [23] examined the

relationship between the prevalence of autoimmune dis-

orders in celiac disease and the duration of exposure to

gluten. Over a 6-month period, 909 patients with celiac

disease were enrolled (group A), 1268 healthy controls

(group B), and 163 patients with Crohn’s disease (group

C) were evaluated for the presence of autoimmune dis-

orders. In all cases the diagnosis was confirmed by typi-

cal radiological, endoscopic, and histological criteria. In

most cases, the disease was localized to the ileum and

cecum; 47 subjects only had colitis and 9 had multiple

localizations. All patients had undergone at least one

course of immunosuppressive therapy (with corticoster-

oids, azathioprine, or both) before entering into the study.

The results indicated that the prevalence of autoimmune

disorders in group A was significantly higher than in

group B (14% vs. 2.8%) but not higher than in group C

(12.9%). Prevalence of autoimmune disorders in celiac

disease increased with increasing age at diagnosis. In a

logistic regression model, age at diagnosis was the only

significant predictor variable of the odds of developing

an autoimmune disorder. This study indicated that the

prevalence of autoimmune disorders in adolescent and

young adult patients with celiac disease was significantly

higher than in the general population, confirming previ-

ous reports in adults [127-130].

The duration of exposure to gluten plays a pivotal role

in the development of autoimmune disorders in patients

with celiac disease: the sequence of diagnosis of auto-

immune disorders and celiac disease and the effect of

exposure to gluten during a challenge test for diagnostic

purposes. In 77.5% of the 147 cases in which celiac dis-

ease and autoimmune disorders were associated, the di-

agnosis of an autoimmune disorder was made first; i.e.,

the autoimmune disorder developed in a condition of un-

recognized and untreated celiac disease. This agrees with

the findings of many reports [128,129,131-133]. In con-

clusion this data show for the first time that the preva-

lence of autoimmune disorders in celiac disease is related

to the duration of exposure to gluten.

4.7. Advances in Celiac Disease and Gluten Free

Diet

All foods and medications containing gluten from wheat,

rye, and barley, and their derivatives are eliminated, as

even small quantities of gluten from diet may be harmful.

Complete removal of gluten from the diet in a patient

with celiac disease will result in symptomatic, serologic

and histological remission in the majority of patients

[134-137]. Green and colleagues [138] showed that 70%

of patients reported an improvement in symptoms within

2 weeks of initiating the gluten-free diet.

Some patients have been found to suffer from refrac-

tory celiac disease in which patients may not respond

entirely to the gluten free diet [44,139].

A gluten-free diet is complex: sources of hidden gluten,

balanced meal planning, label reading, shopping for

foods, dining out and traveling, benefits of exercise and

relaxation, appropriate vitamin and mineral supplementa-

Safety Food in Celiac Disease Patients: A Systematic Review 65

tion, credible resources and support groups.

Also, family members must understand the importance

of taking precautionary measures to prevent cross-con-

tamination of foods. Gluten-free foods must be stored

and prepared separately, cooking and serving utensils

must be cleaned carefully prior to use, and a separate

toaster must be purchased for the person with celiac dis-

ease.

When a patient begins to eat gluten-free, there is often

much concern and confusion as to which foods are al-

lowed and which are not. Many foods are gluten-free,

such as milk, butter and cheese, fresh, frozen or canned

fruits and vegetables, fresh meats, fish, poultry, eggs,

beans, seeds, nuts, corn, and rice. Gluten is predomi-

nantly present in breads, cereals, and pastas but is sur-

prisingly found also in seasonings, sauces, marinades,

soy sauce, soups, salad dressings, and conveniently pack-

aged flavored rice. It is critical that a patient ensures that

each product is gluten-free by carefully reading food

labels or by contacting food companies.

Eating and baking gluten-free has become easier in

recent years, with increases in the number and quality of

gluten-free food products that are available on-line and in

some food stores [140].

Gluten-free baked goods tend to be high in fat and

calories to enhance flavor, texture, appearance and over-

all acceptability of the gluten-free products, which may

be of concern for those patients who do not wish to gain

any weight [84,140].

Aside from meeting their daily fiber needs, it is also

important that people with celiac disease consume ade-

quate daily amounts of thiamin, riboflavin, niacin, folate,

iron, calcium, and fiber [141]. People with celiac disease

must read all food labels to ensure the gluten-free status

of a food item. This process has become easier since the

FALCPA of 2004 [142] requires that all food products

manufactured after January 1, 2006, be clearly labeled to

indicate the presence of any of the top eight food aller-

gens (milk, eggs, fish, crustacean shellfish, tree nuts,

peanuts, soybeans, and wheat). This act has simplified

label reading by identifying those foods that contain hid-

den wheat gluten.

Each study determined a different safe threshold for

which gluten-contamination should be set: 100 parts per

million (ppm) per day (equivalent of 30 mg gluten) [18],

between 10 and 100 mg intake daily [92] and 50 mg per

day in the treatment of celiac disease [93]. A unanimous

view is that gluten free dieting should be as strict as pos-

sible a diet completely devoid of gluten would be diffi-

cult if not impossible to maintain [18,92,93].

The US FDA [143] is proposing to define the food-

labeling term gluten-free to mean that a food bearing this

claim does not contain an ingredient that is a “prohibited

grain” (e.g., durum wheat, spelt wheat, or kamut etc.), an

ingredient (e.g., wheat flour) that has not been processed

to remove gluten and an ingredient that is a “prohibited

grain” (e.g., wheat starch) but has been processed to re-

move gluten.

Most European countries have accepted the definition

of gluten-free designated by CODEX Alimentarius [144].

CODEX has established that the content of gluten in

gluten-free products (free of wheat, rye, and barley)

should not exceed 20 ppm, while those food products

containing ingredients from wheat, rye, or barley that

have been rendered gluten-free must contain 200 ppm

gluten.

4.8. Safe Gluten Threshold for Patients with

Celiac Disease

A long term of a GFD is associated with clinical, sero-

logic, and histological remission [135], but it is almost

impossible to maintain a diet with zero gluten content

because gluten contamination is very common in food.

“Hidden” gluten may be found in commercially available

products, such as sausages, soups, soy sauces, and ice

cream. Even products specifically targeted to dietary

treatment of CD may contain tiny amounts of gluten

proteins, either because of the cross-contamination of

originally gluten-free cereals during their milling, storage,

and manipulation or because of the presence of wheat

starch as a major ingredient. The potential toxicity of

trace amounts of gluten is still unclear.

In CD patients the ingestion of 100 - 500 mg gliadin/

day for 4 week, is able to cause measurable changes in

the architecture of the small-intestinal mucosa [145].

Only limited data are available on the toxicity of lower

doses of gluten [25,146-148]. Establishing a safe thresh-

old of gluten consumption for CD patients is more im-

portant because the high prevalence of the disease world-

wide [149,150].

The “gluten threshold” topic is currently under evalua-

tion by the Codex Alimentarius, the WHO/FAO commis-

sion that is in charge of setting food standards at the in-

ternational level.

A recent Italian study was to establish the safety

threshold of prolonged exposure to trace amounts gluten.

This study was a prospective, multicenter placebo-con-

trolled, double-blind, randomized trial performed be-

tween the years 2001 and 2004. The patients were adults

with biopsy-proven CD who had consumed a GFD for 2

years and were in apparent good health. Control subjects

were adults who were negative for serologic CD marker

sand for Helicobacter pylori and were undergoing upper

endoscopy for diagnostic purposes. They were asked to

maintain a strict GFD during the study period, avoidance

of any possible source of gluten contamination (such as

restaurant meals). The only cereal-based food they were

Safety Food in Celiac Disease Patients: A Systematic Review

allowed to eat was the special GFD products on the mar-

ket in Italy, which Italian law establishes having a gluten

contamination of 20 ppm (20 ppm = 20 mg/kg product).

After 1 month, subjects returned for a baseline evaluation.

While still adhering to a strict GFD, the patients were

randomly assigned to ingest for 90 days a capsule con-

taining either 10 mg purified gluten, 50 mg purified glu-

ten, or 50 mg cornstarch as a placebo. After completing

the three months micro-challenge, the patients repeated

the same clinical, serologic, and histological tests. In this

study, the analysis of the effects of the gluten micro-

challenge suggested that the villous height/crypt depth

(Vh/Cd) Index reflected more closely the damage in-

duced by traces of gluten in the diet than did the IEL

count. The baseline duodenal biopsy results showed evi-

dence of histological damage (decreased median Vh/Cd

and increased median IEL count) in adult CD patients

receiving long-term dietary treatment [93]. Furthermore

4 of 49 subjects had to be excluded from the protocol

because severe enteropathy was detected at the baseline

evaluation. These results confirm that abnormal small-

bowel morphology persists in a significant proportion of

CD patients treated with a GFD, despite full resolution of

their symptoms [18,151,152]. Some CD patients showed

a clear-cut worsening of the small-intestinal architecture

after ingesting only 10 mg gluten/day, whereas others

had an apparent improvement in mucosal histology after

the three months challenge with 50 mg gluten/day; none

of the 13 subjects receiving 50 mg gluten/day had clini-

cal evidence of relapse. Because of the limited number of

patients, the authors were not able to reach firm conclu-

sions about the potential toxicity of 10 mg gluten/day,

which remained a “gray” micro-challenge to 3 months.

Moreover it is well known that mucosal deterioration

may become manifest after a longer gluten challenge

[153]. Reactions to gluten are not only influenced by the

quantity but also the quality of the ingested protein,

which may change according to cereal variety [154] and

food processing (raw versus cooked grain, fermentation,

etc.) [155] .

The effects of a low gluten intake in CD patients have

been investigated in a limited number of studies. P. J.

Ciclitira et al. [146] analyzed the toxicity and time re-

sponse of a gliadin dose (the major toxic fraction of glu-

ten) in a single patient. They concluded that 10 mg pro-

duced no change, 100 mg a very slight measurable chan-

ge, 500 mg a moderate change and 1 g extensive damage

to small-intestinal morphology. The same group also re-

ported that the ingestion of 2.4 - 4.8 mg gluten/day

caused no change in the jejunal biopsy morphometry of

treated CD patients after either 1 or 6 week [156,157]. J.

Ejderhamn et al. [123] showed that a daily intake of 4 -

14 mg gliadin did not affect the morphology of the small

bowel mucosa in CD patients receiving long-term treat-

ment with a GFD. Recent Finnish studies indicate that an

intake of 20 - 36 mg gluten/day has no detectable effect

on mucosal histology [25,124]. While in a previous study,

the authors showed that a 4-week challenge with 100 mg

of gliadin/day caused deterioration of the small-intestinal

architecture and that the histologic changes were more

pronounced in patients challenged with 500 mg gliadin/

day [158].

Finally, a higher gluten intake (1 - 5 g/day), still lower

than the normal gluten intake for the non-CD population

in Western countries (10 - 20 g/day) [158] caused relapse

of disease at a clinical, laboratory, and histological level

both in children and in adults [159,160].

On the basis of the evidence from the Italian study [87]

and the quoted literature, it appears that 50 mg gluten/

day is the minimum dose required to produce measurable

damage to the small-intestinal mucosa in CD patients.

Currently, different national positions hamper the im-

plementation of uniform guidelines on the maximum

level of gluten contamination (expressed as ppm) that

can be tolerated in products that are marketed for the

treatment of CD [94,161]. In Northern European coun-

tries, up to 200 ppm gluten is permitted in food for CD

patients, to use wheat starch as ingredient. Instead, a

more prudent value of 20 ppm has been adopted in North

American and southern European countries. Finnish ex-

perts advocated the intermediate limit of 100 ppm [143].

The decision about what the threshold is depends, how-

ever, not only on the minimum toxic dose but also on the

amount of gluten-free products consumed.

The results of C. Catassi study [87] indicate that 200

ppm is not a safe threshold because the harmful gluten

intake of 50 mg/day could be reached even with a mod-

erate consumption of nominally gluten-free products,

especially in countries such as Italy, where consumption

of wheat substitutes is occasionally as high as 500 g/day.

The threshold of 20 ppm keeps the intake of gluten from

“special celiac food” well below the amount of 50 mg/

day, which allows a safety margin for the variable gluten

sensitivity and dietary habits of patients. The protracted

intake of 50 mg gluten/day produced significant damage

in the architecture of the small intestine in patients being

treated for CD.

5. Conclusions

At this time, the gluten-free diet remains the only avail-

able treatment. The gluten-free diet is a complex and

challenging diet but recent advances in the food industry

are making it easier to follow. Patients who understand

the long-term consequences of celiac disease will make

informed choices in managing their disease. Dietitians

provide the tools that patients need to successfully un-

derstand the diet and integrate it into every aspect of their

lives, leading to overall improvements in the physical

Safety Food in Celiac Disease Patients: A Systematic Review 67

and emotional challenges of the disease. Unfortunately,

several studies shows that abnormal small-bowel mor-

phology persisted in a significant proportion of CD pa-

tients being treated with a GFD, most likely because of

the persistent ingestion of trace amounts of gluten. The

protracted intake of 50 mg gluten/day produced signifi-

cant damage in the architecture of the small intestine in

patients being treated for CD. However, the sensitivity to

trace intakes of gluten showed large inter-patients vari-

ability, a feature that should be accounted for in the im-

plementation of a safe gluten threshold. Gluten ELISA

are able to detect gluten contamination in foods in many

instances and are a valuable tool in the analysis of GF

foods. However, they are not clinically validated as an

indicator of food toxicity toward CD patients and ana-

lytical-based predictions of food toxicity are not straight

forward. These methods cannot, in our opinion, ensure

the safety of GF foods but must be employed with ap-

propriate precautions. False reliance on the methods is to

be avoided if official standards for GF foods based on

final gluten content are widely adopted. Based on a con-

sideration of the diet of celiac patients, current data indi-

cate that wheat starch-based food is safe, provided it

contains <100 mg gluten/kg. Furthermore, there is no

evidence to support a definition of naturally gluten-free

requiring no detectable gluten (i.e. a “zero tolerance”).

Gliadins trigger celiac disease, but they are also major

allergens of food allergy to wheat, capable of provoking

IgE-mediated reactions. Measurement of gliadins there-

fore constitutes a good estimate of the amount of gluten

and of wheat proteins in products containing wheat. In

recent years, more reliable and sensitive assays to deter-

mine the presence of gliadin in foods have been devel-

oped and commercialized. These are either based on the

detection of the heat-stablex-gliadins or on the detection

of a “toxic” motif in gliadin (the so-called R5 antibody

assay). The evidence obtained through recent studies in-

dicates that the maximum tolerated daily dose of gluten

for celiac disease patients would also constitute a base

for a safe upper limit per serving for the vast majority of

sufferers from wheat allergy [92]. D. Schuppan et al.

[159] recently reviewed the intensive search for novel

therapies to treat CD. In spite of these ongoing efforts,

GFD remains the cornerstone of CD therapy. Adherence

to a GFD may be difficult for a significant number of

celiac subjects for a variety of reasons. The inclusion of

oats into a GFD is desirable for their nutritional value,

but it also remains controversial [160]. Contamination of

oat grains and oat products with prolamins from other

cereals is a frequent issue, and pure oats are not widely

available. Another reason for intolerance to oats is the

wide range of susceptibility to gluten peptides of differ-

ent cereals in individuals with CD. Significant success

was achieved in Canada through the cooperation of gov-

ernment-supported agencies and the Canadian Celiac

Association. Their incentive facilitated the offering of

uncontaminated oat products and foods to Canadian ce-

liac in 2005 [161]. At present, similar initiatives are un-

derway in other countries, particularly in Finland. The

terms “100% oats,” pure oats” or “organic oats” do not

guarantee that the product is free of contamination [60].

In general, Scandinavian countries have been observed to

be more liberal with the use of oats in comparison with

Mediterranean countries. Future efforts should be aimed

at the following topics:

1) Selecting oat cultivars with a low avenin content

and/or low stimulatory activity of intestinal T cells. Only

these cultivars should be used in agricultural processing

and the production of raw materials and foodstuffs;

2) Research and development of recombinant oat va-

rieties complying with these requirements;

3) Development of new assay methods to detect aven-

ins in oat products;

4) Creation of guidelines for the agricultural process-

ing of oats and industrial manufacturing of oat products,

as well as for clinical follow-up of celiac consuming oat-

enriched GFDs.

Future directions in CD research have been clearly

identified and were recently discussed both at the 9th

International Symposium on CD that was held on August

10-13 in Baltimore [162] both at the first World Con-

gress of Pediatric Gastroenterology, Hepatology, and Nu-

trition in Boston [163]. Although some of these goals are

in an advanced state of development (i.e. engineering

gluten-free grains) others (i.e. the search for the CD

genes) are extremely challenging and will require an in-

ternational task force to generate meaningful data. Nev-

ertheless, the appreciation that CD is not a disease con-

fined in Europe but a global problem affecting continents

such as North and South America, Africa and Asia,

where it was historically considered an extremely rare

condition.

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Safety Food in Celiac Disease Patients: A Systematic Review

Abbreviations List

CD: celiac disease;

GFD: gluten-free diet;

IF-



: interferon-



;

TNF-



: tumor necrosis factor-



;

RCD: refractory celiac disease;

IELs: intraepithelial T lymphocytes;

EATL: enteropathy associated T-cell lymphoma;

IL-10: interleukin-10;

tTG: tissue transglutaminase;

FDA: food and drug administration;

FALCPA: food allergen labeling and consumer protec-

tion act;

ppm: parts per million;

HACCP: hazard analysis and critical control points;

ELISA: enzyme-linked immunosorbent assay.